Currently, inertial guidance sensors operate in many flying aircraft for guidance of the aircraft. Ring laser gyros are used as inertial guidance sensors in aircraft as well as ships, submarines, satellites, missiles and other vehicles. However, when the vehicle enters a radiation environment, the radiation affects the sensor and hampers the operation of the sensor and as a result, guidance is hampered. Specifically in ring laser gyros, the laser discharge that keeps the ring laser gyro operating must remain ionized for the operation of the gyro to be maintained. Proper operation of the ring laser gyro requires that the laser discharge not be extinguished when the ring laser gyro is exposed to a radiation environment. The laser discharge is maintained by a high voltage power supply whose operation can be interrupted by the radiation environment. Specifically, a prompt gamma ray pulse can cause the high voltage power supply voltage to fall below the value required to maintain the laser discharge. When this happens, the vehicle being guided by the ring laser gyro can go off its planned course and be prevented from accomplishing its mission.
High voltage power supplies that use pulse width modulators to produce the required high voltage are susceptible to prompt gamma pulse upsets that reduce the high voltage below the level required to maintain lasing in the ring laser gyro. This occurs when the prompt gamma pulse turns off circuits internal to the pulse width modulator, specifically turning off an error amplifier used to determine the duration of the pulse width modulator output pulses which decreases voltage supplied and interrupts ring laser gyro operation.
FIG. 1 shows the effect on the high voltage supply output voltage of a simulated prompt gamma ray pulse. The prompt gamma ray pulse was simulated using a flash x-ray radiation source. As can be seen, the radiation pulse reduced the high voltage output below the level required to maintain the laser discharge (this voltage is about 450V for this experiment). Once the laser discharge is extinguished, it is not easy to re-initiate and the vehicle that depends on the ring laser gyro for navigation information is essentially blind and out of control until the discharge is re-initiated. Current methods used to maintain the laser discharge rely on expensive radiation hardened components. However, the radiation hardening techniques have not been shown to prevent dose rate: induced upsets of internal components. It would be beneficial to maintain the power supply output at acceptable levels so that operation of the ring laser gyro is not interrupted. It would be beneficial to have a less expensive means to maintain the power supply as well.